Abstract

The aim of the present study was to assess the effect of cold water immersion (CWI) on postexercise parasympathetic reactivation. Ten male cyclists (age, 29 ± 6 yr) performed two repeated supramaximal cycling exercises (SE1 and SE2) interspersed with a 20-min passive recovery period, during which they were randomly assigned to either 5 min of CWI in 14°C or a control (N) condition where they sat in an environmental chamber (35.0 ± 0.3°C and 40.0 ± 3.0% relative humidity). Rectal temperature (Tre) and beat-to-beat heart rate (HR) were recorded continuously. The time constant of HR recovery (HRR) and a time (30-s) varying vagal-related HR variability (HRV) index (rMSSD30s) were assessed during the 6-min period immediately following exercise. Resting vagal-related HRV indexes were calculated during 3-min periods 2 min before and 3 min after SE1 and SE2. Results showed no effect of CWI on T re (P = 0.29), SE performance (P = 0.76), and HRRt (P = 0.61). In contrast, all vagal-related HRV indexes were decreased after SE1 (P < 0.001) and tended to decrease even further after SE2 under N condition but not with CWI. When compared with the N condition, CWI increased HRV indexes before (P < 0.05) and rMSSD30s after (P < 0.05) SE2. Our study shows that CWI can significantly restore the impaired vagal-related HRV indexes observed after supramaximal exercise. CWI may serve as a simple and effective means to accelerate parasympathetic reactivation during the immediate period following supramaximal exercise.